Automatic volume control



May 21, 1935. H. A. WHEELER AUTOMATIC VOLUME CONTROL Filed Aug. 14," 1931 ATTO RN EYS Patented Ma 21, 1935 UNITED STATES AUTOMATIC VOLUME CONTROL rial-01a A.

Wheeler, Great Neck, N. Y., assignor to Hazeltine Corporation Application August 14, 1931, semi No. 550,979

19 Claims. ((21. 250-20 6 determined level.

Various systems for providing automatic volume control have been developed which continuously adjust the gain of the amplifier stages of a radio broadcast receiver, so that the signals .are reproduced with substantially even volume regardless of the strength of the carrier frequency input energy to the receiver. However, the present systems, which obtain automatic volume control of the received radio signals involve sup-' plying the detector with a large amplified signal voltage. This large amplified signal voltage is necessary in order that the fiuctuationsin the grid biasing voltage of the tube upon which the automatic volume control acts shall be sufficiently large adequately to control the volume through a considerable range of amplification ratios.

And large amplified signal voltages require the use of a considerable number of amplification stages prior to the detection stage of the receiver.

It is the object of the present invention to overcome the above noted objection to the ordinary automatic volume control receiver and to provide an automatic volume control for a radio receiver which does not require a large amplified signal voltage to be supplied to the detector in order to obtain a sufilciently large variation in the bias of the amplifiers.

A disadvantage which is common .to radio re-' ceivers employing an automatic volume control, is that they are sensitive to .surges or pulses, causing what is known as motor boating.

Therefore, it is a secondary object of the present invention to provide a balancing circuit which is adjusted in both amplitude and phase to cancel the modulation effects due to undesired fiuctuations in the source of direct voltage for the anodes of the tubes which receive the automatic volume control bias, which fluctuations produce the motor boating effect.

In accomplishing the objects-of the-present invention, a sensitive grid-leak detector and an added D. C. amplifier tube are used. The latter tube, which is hereinafter called the.volume control tube, per-forms three functions: It amplifies or repeats the changes of potential occurring in the detector plate circuit; it reverses the direction of the changes;' and it supplies the re-' sulting changes as'an automatic control grid bias to one or more of the tubes preceding the detector.

These functions are accomplished'with a common 'justecl by varying the operating potentials of the automatic volume control tube, as will be described hereinafter.

The object of the invention relative to the prevention of motor boating is accomplished by varying the bias of one or more radio frequency amplifier tubes by an amount sufficient to compensate for the variation in plate potential, the variation in bias being out of phase with the variation in plate potential.

Attention is now invited to the drawing in which the single figure shows a circuit diagram of a signal responsive system in the form of a radio receiver incorporating a fluctuation compensating networkaccording to the present invention. p w

The carrier frequency current is impressed upon the radio frequency amplifier I! by the antennacircuit, which includes the antenna l0 and the ground ll. As indicated in the drawing, the carrier frequency amplifier comprises four tuned radio frequency coupling systems I3, which are tuned simultaneously by means of condensers and a uni-control mechanism which are not shown. These coupling systems include three radio frequency amplifier tubes H. The gain of amplifier I2 is controlled'by the bias voltage on the grid, or control electrode, of one or more of the tubes M. This is accomplished by means which will be described hereinafter.

The radio frequency amplifier 12 may be replaced by a superheterodyne arrangement or any other amplifying arrangement, the specific details of which constitute no part of the present invention.

If triode vacuum tubes are used in amplifier i2. itmay be advantageous to neutralize the inherent grid plate capacity coupling 'by one of the well known neutralization circuit arrangements.

Screen grid tubes may also be used, in which case neutralizing means will be unnecessary. p

The output of the radio frequencyamplifieri I2 is connected to a detector, or rectifier, circuit which circuit produces a uni-directional voltage dependent on the impressed alternating current signal strength. The circuit utilizes the familiar type of detection which is commonly referred to 60 asgrid current rectification. The detector cirode, and the primary coil of the audio frequency transformer 29, for coupling the audio frequency output of the detector to the audio frequency amplifier.

The output of the transformer 29 is applied directly to the high resistance potentiometer or voltage divider 33. By this means any desired portion of the total secondary voltage of transformer 23 may be applied to the grid of the audio frequency amplifier tube 22. The amplifier 22:

is in turn coupled through the audio frequency transformer 33 to the grids of a push-pull amplifier comprising the two tubes 23. The output of the tubes 23 is coupled through audio transformer 33 to the voice coil of loud speaker 31. The circuits so far described operate inthe manner well known in the art and need no further description. 1

The grid and the plate, or anode, potentials for the various tubes of the receiver are supplied preferably by a unitary source ofdirect voltage from filtered rectified alternating current. The positive output terminal of the alternating current power supply rectifier (not shown) is connected to terminal 53 and the negative terminal is connected to terminal 59. The ripple filtering system comprises the three high capacity condensers I1 and the choke coils l5 and 53 connected as shown. One of these coils, as for example 55, may also serve as the field magnetizing coil of the speaker 31, if such a magnetizing coil is required in the speaker to be used. The required direct voltages for operating the receiver are obtained by use of a group of resistances 50, ii, 32, 53 and 34, which are connected in series between the posirectifier and filter system.

Theradio frequency amplifier plate, or anode, voltages are supplied through lead 65 which is connected to the point between resistances 5! tion point between resistors 52 and 33.

The detector plate potential is supplied through the lead 66, connected to the terminal 33. Included in this lead is the resistance 28 which cooperates with the audio frequency by-pass condenser 21, to reduce the fiow of any residual ripple current in the plate circuit of the detector The plate current of the audio frequency amplifier tube 22 is also supplied by the lead 83 from the terminal 53. This latter connection is made through a resistance 32. An a 0 frequency by-pass condenser 3| is provided as own connected between the cathode of amplifier tube 22 and the end of the. primary coil of the output transformer which is remote from the anode of the same tube. The grid bias potential for the amplifier 22 is supplied by the lead 33, connected to the iunctioii of resistances II and 54.

r The plate voltage of the pushepull amplifier stage including the tubes 23,1.is supplied directly from the connection 33 to the high potential'end the tube 42.

v 2,001,950 frequency currents between the plate and cathof the filter. The grid biasvoltage of this stage is obtained from connection 30 and is rendered free of ripple by means of series high resistance 35 and the by-pass condenser 34. The cathodes of this stage are not grounded, but are kept at the correct potential by means of lead 6|, which is connected as shown between the chokes 55 and 33.

The detector circuit, including tube 2i, is designed to give substantially linear relationship between percentage modulation and audio frequency output, providing the carrier input voltage applied to the grid condenser 24 is in the neighborhood of from one-half to two volts. Thisis accomplished by the use of a high resistance grid-leak 23 which permits a negative rectified voltage on the grid nearly equal to the peak value of the applied radio frequency voltage. Overloading, due to excessive reduction of the plate current by the rectified negative grid voltage, is' reduced to a minimum by supplying'the plate current from high voltage lead 66 through the high resistance 23. The result is that an increased value of negative voltage on this grid is f largely compensated forby the increasing positive voltage on the plate. It is observed that, owing to the resistor 23, the voltage of the plate, or output electrode of the tube is less positive than the plate voltage supply thereof at terminal 58, but changes positively when the signal strength increases.

The circuit of the automatic volume control tube 42 will now be described. The volume control tube 42 'is a triode including the usual cathode, grid and anode. It acts as an amplifier or repeater of changes in potential at point 4i in .the detector plate circuit. tive and negative terminals 33 and 59 of the Connected to the point 4l in the detector plate circuit is a lead 62 connected to the low potential end of the filter voltagedivider. Included in this lead are resistances 33 and 38 in series, the Junction point of which is connected to the grid of Because of the connection of resistor 38 (in a circuit across the direct voltage source) between points 40 and 4|, the output electrode of the detector is maintained at a voltage which is substantially positive relative to the input, or control, electrode of the volume control tube 42. The cathode of the volume control tube is connected to a variable tap on the resistor 50, by which means the bias of the grid of the volume control tubecan be accurately adjusted,

trol electrode of the volume control tube is normally (i. e.' in the absence of signal output from the radio frequency amplifier) maintained at a voltage slightly more negative than that of the cathode thereof. The output electrode potential of the volume control tube is supplied by the lead through point 48 and the resistor 43 to ground, which, it is to be noted,'.is substantially positive relative to any point on the resistor 50. It follows that the cathode of tube 42 is maintained at a voltage greatly negative relative to ground. and consequently, relative to the cathodes of amplifier |2. The-point 43 is also connected to the control grids of the amplifier, through the resistor 44, thus providing 'a direct-current connection from the anode of the volume control tube to the said grids. Thus the point 43 and the anode of the volume control tube 42 are positive relative to both the cathode andgrid of tube 42 but theanode of tube 42 is normally maintained slightly negative relative to thecathdes of amplifier l2 because of the voltage across resistance 43'. The grid bias connections of the tubes M are returned to ground through radio frequency bypass condensers II and radio frequency couplings from one circuit to another are prevented by means .of resistors l6, which, however, do not impede the fiow of direct current.

It is observed that each of the control tube 42 is connected to a point of the unitary voltage source which is maintained, by an individual connection to the unitary voltage source, more negative than the most negative electrode of the detector tube.

The point 41 in the grid bias connection is connected to the lead 64, which is a point more negative than ground, through resistor 45 and condenser ,the function of which will be described later.

The operation of the present invention will now be described.

The initial value of the potential at the point ll which is the grid bias potential of the tubes I4 is adjusted by means of the contact on the resistor 50 whichdetermines the negative volt-' age of the cathode of volume control tube 42, and therefore the grid bias of the latter tube. In

' the absenceof any incoming'si gnal, this contact is adjusted so that the meter 20, which indicates the value of the plate current'in the tubes N, indicates the maximum permissible degree of amplification} In other words, the adjustment of the potential of lead 49 effectively varies the grid bias of the tube 42, and, therefore, varies the current in the plate circuit thereof through the resistance 43. This latter, of course, varies the potential of the point 48, which thus may be adjusted to the required grid bias potential.

Having performed this adjustment, a signal is received by tuning the amplifier l2, and the amplified carrier frequency voltage is impressed on the detector 2|. This causes a uni-directional change ofvoltage, namely a decrease in the detector plate current which decreases the potential differencebetween the point ll and the connection '86. In other words, the potential of point it and of the output electrode of the detector 2|. becomes more positive in the presence of an amplified signal from the preceding amplifier 12. The average current of the detector output electrode changes in response to increasing the signal output of said amplifier, by an amount which is substantial as compared with the current flowing in the path comprising resistors 28, "and 39. Consequently, the voltage on the said output electrode likewise changes by an. amount 7 which is substantial as compared with the voltage difference between the detector output electrode and the control electrode of volume control tube 42.

Part of'this positive change occurs also at point ll, where it is applied to the grid of the volume-control tube 42, with the result that the control electrode of the volume control/tube becomes proportionally more positive in the pres-- nal applied to the detector. is maintained sub-.

the electrodes of I 'the signal is substantially unaflected. At the same time it is sufflciently responsive to materially reduce the eflect of fading, and also to respond to changes in the intensity of the signal being received as the set is tuned from one station to another. The action of the automatic volume control, which tends to produce an audio output signal of the same mean intensity-regardless of the intensity of the received'signal, makes it difficult to observe by. ear the correct setting of the tuning control associated with the radio frequency transformers It. For this rea-' son, the meter 20 is associated with the radio frequency amplifier l2. The meter 20 may be observed to assist in obtaining the correct tuning point. .In this function the meter 20 is commonly referred to as a tuning meter, which isnow well known in the art.

Since the signal input to the detector is maintained substantially unvarying, it is necessary to adjust the gain of the audio frequency amplifier in order to adjust the intensity level at the loud speaker 31. This volume level control function is performed by the voltage divider '30 in a well known manner. J

The degree to which the tube 42 amplifies the fluctuations of potential at the point ll may be somewhat increased by utilization of a regenerative action" which is inherent in this circuit. At the same time this action must not exceed a certain maximum permissible value, because the tube 42 would then be subject to a trigger effect and the circuit, as a whole, would be inoperative. with the circuit constants, which will be given in detail below, this regenerative eifect is utilized to auseful but not excessive degree. The theory of this action is as follows: A positive change in the potential at point 40 causes a negative change in the potential at point 48 and adecrease in the plate current of tubes ll. This decrease in the plate current is relatively large, which results in an increase in the current through rethere is caused thereby a positive change of all potentials inthe voltage supply system. This in turnproduces a positive change. of the potential of point 40, which aids the initial positive change which was assumed to be applied thereto.

'Inthis receiver, when working the push-pullstage at high output levels, the re ulting disturbance of the source of direct vol e having the undesired fluctuations tends to modulate the tubes ll in the amplifier l2. This results either in a continuous oscillation. of a low audio frequency above referred to as "motor boating," or in distortion of the received-signal. In accordance with one of the vobjectsof'f this invention,

the. modulation tendency is-reduced to a minimum by employing a modulation balance through condenser 46 and resistor By this means there is superlmposedupoii the grid bias potential a modulating fluctuation which is equaland opposite in effect as compared with'themodulatlng' action of thefluctuations in the plate voltage of the tubes ll. Of the -two elements ll and ll,

the condenser is the more important. The;

resistance 45 serves principally to correct the phase of the fluctuation superimposed on the grid bias voltage. "It is observed that the eie 118 resistor I! (R3).

orderthat the modulation balance may be effective, it is necessary that the audio frequency amplifier tubes shall not be connected to any point on the resistors l2 and '3; otherwise, this balance action might be materially disturbed.

In these equations: 1

Rl=resistance 52 R2=resistance 53 R 3=resistance 45 C1=total of capacities 1'7 C2=total of capacities 15 C3=capacity 46 Mu=amplification factor of tubes 14 Equation (1) above is ordinarily the more important, and does not involve the phase-correct- For best results, however, this resistor must have the correct value to satisfy Equation (2).

The vacuum tubes used in connection with the circuit comprising the present invention might be of any type, and any means for heating the cathodes of the same may be provided. It is understood, of course, that whereas any of a number of types of tubes are effective and similar in operation, those employing an indirectly heated cathode, such as type 221, are preferred, in which, case the heaters are. connected to a secondary of the alternating current power transformer which supplies power to the rectifier. Thwe type 221 tubes have an amplification factorfof approximately 9. In the pushpuil stage, tubes 23 are preferably of type 245. Although it is understood that a wide variety of circuit constants may be employed in a device operating in accordance with the invention just dwcribed, the following constants have bee found to be satisfactory:

By-pass condensers I! .1 microfarad Resistors IO 1,000 ohms By-pass condensers I'I .1 microfarad Resistor l 1000 ohms Grid condenser 24 50 micro-farads Grid-leak 25... 2 megohms Plate condenser 26 .002 microfarad By-pass condenser 21 1 microfarad Resistor 2! 50,000 ohms Potentiometer IL--- .5 megohm By-pass condenser 3L; .5 microfarad Resistor 32 25,000 ohms By-pass condenser 34 .1 microfarad Resistor 35 .25 megohm Resistor 3| .5 megohm Resistor 39 .l megohm Resistor 42 50,000 ohms Resistor 44 .25 megohm Resistor l 5,000 ohms Condenser 46 .5 microfarad Resistor I 2000 ohms Resistor ll 2000 ohms Resistor" 5300 ohms Resistor 53 950 ohms Resistor l4 400 ohms Choke ll 800 ohms (Iron-core choke-Speakerfield) -Chohe il.. 550 ohms (Iron-core choke) 2,001,950 ment It is connected to the connection 04. In

The transformer 20 may preferably have a 1:4 ratio. The meter 20 may havea 15 milliampere range.

With the above constants the following voltages will be deveiopedat the stated leads when a difference in potential of 270 volts exists between points 58 and II:

I: +140 volts The potential of 49 lies between --37 and 30 volts, depending on the position of the contact of resistance It.

It is obvious, of course, that other constants I may be used in the circuit constituting this invention without departing from the scope thereof as set forth in the following claims.

I claim:

1. A fluctuation compensating network comprising a source of direct voltage having undesired fluctuations, two resistances R1 and R2 connected respectively in series from positive to negative terminals of said source, a capacity C1 in parallel with resistance R1, a. point connected through a capacity C2 to the; junction of said resistors and through a capacity C3 in series with "a resistance R3 to said negative terminal, and a vacuum tube having an amplifying factor Mu, a plate connected to said positive terminal, a grid connected to said point, and a cathode connected to said junction, said elements being related substantially in accordance with the following equations:

2. A signaling system comprising an amplifier connected to a three electrode detector coupled to the output'of said amplifier having a cathode, anode and control electrode, which detector produces a uni-directional change of voltage dependent on the alternating signal voltage impressed thereon, a volume control tube having a cathode, anode, and control electrode, a connection for coupling the said change of voltage to the control electrode of said volume control tube, means for maintaining the cathode of said volume control tube at a potential greatly negative relative to said amplifier cathode, means for maintaining the anode of said volume control tube at a potential normally slightly negative relative to said amplifier cathode, a resistance in series with the anode of said volume control tube for causing thereon a corresponding change of voltage whereby an increase in the current supplied to said rectifier will produce an increase in the anodecathode current through said volume control tube, and a connection from the anode of said volume control tube to the control electrode of said amplifier, whereby the amplification of said amplifier is regulated automatically.

- 3. In a signaling system, a vacuum tube amplifier having a cathode and a control electrode, a vacuum tube detector coupled to the output of said amplifier, said detector having more than two electrodes, including an output electrode, a volume control tube having a cathode, an input and an output electrode, means for maintaining the output electrode of said detector much more means for causing the output electrode said detector to become more positive in the presence of an amplified signal, means ior'causing the input electrode oi. said volume control tube to become proportionally more positive in the presence of an' amplified signal, and a direct current connection between the output electrode 0! said volume control tube and the control electrode oi! said vacuum tube amplifier, whereby the amplification of said amplifier is regulated automatically.

4. In a signaling system, a vacuum tube amplifier having a cathode and a control electrode, a vacuum tube detector coupled to the output of said amplifiena volumecontrol tube coupled to the output-oi said detector, said volume control tube having a cathode and an output electrode, means for maintaining the cathode of said volume control tube greatly negative relative to said amplifier cathode, means for maintaining the output electrode of said volume control tube normally slightly negative relative to said amplifier cathode, means for causing said output electrode to become more negative in the presence of an amplified signal, and a direct current connection between said output electrode and said control electrode, whereby the amplification of said amplifier is regulated automatically.

5. In a signaling system, a vacuum tube amplifier having a cathode and control electrode, a vacuum tube detector coupled to the output or said amplifier, said detector having at least two electrodes, including an output electrode, a volume control tube having input and output electrodes, means for maintaining the output electrode of said detector substantially more positive than the input electrode of said volume control tube, means for maintaining the input electrode of said volume control tube more negative than the cathode thereof, means for causing the output electrode of said detector to become more positive in the presence of an amplified signal,

thereby causing the input electrode or said volume control to become proportionately more positive in the presence of an amplified signalaa direct current connection between the output electrode or said volume control tube and the control electrode 0! said vacuum tube amplifier, whereby the amplification of said amplifier is regulated automatically, and an alternating current coupling between the control electrode or said amplifier and a point on the source 01' direct current for. said amplifier, whereby voltage fluetuations or said source are coupled to the control elecgde oi said'amplifier to compensate for the fiuc 'tions in amplification occasioned-by said fluctuations of said source.

6. In a signaling arrangement, a signal responsive system including a vacuum'tube having a control electrode, a detector tube coupled to the output oi said system, a control tube having an anode, cathode and control electrode, a direct current connection between said anode'and the control electrode of said vacuum tube, a. unitary source oi direct voltage for said tubes, and three resistors connected in series between the positive and negative terminals or said source, the output or said detector being connected to a point between the first and second of said resistors, andthe junction of the second and third resistors being connected to the control electrode of said control tube, whereby the uni-directional component of the rectified current output 0! said detector, due to signals present in said system, acts upon said control tube to cause it to automatically regulate'the responsiveness of said system to said signals. I

7. A signaling arrangement according to claim 6, in which each of the electrodes of said control tube is maintained, by an individual connection to said unitary source, more negative than the most negative electrode of said detector tube.

'8. A radio signal receiving apparatus which comprises a carrier current amplifier having a grid electrode, a detector tube having a cathode and an anode, a volume control tube having an input electrode and an output electrode, a resistor connected between said anode and a point of a source of direct voltage, for maintaining said anode more negative than said point, a connection including two resistors in series from said anode toa point of said-source, which is more negative than said detector cathode,.a connection .become more negative.

9. A, radio signal receiving apparatus which comprises a carrier current amplifier having a grid electrode, a detector tube having a cathode and an anode, a volume control tube having an input electrode and an output electrode, a resistor connected between said anode and a point of a source of direct voltage, for maintaining said anode more negative than said point, a connection including two resistors in series between said anode and a point of said source which is more negative than said detector cathode, a connection from said input electrode to the point between said two last-mentioned resistors, a connection including a resistor between said output electrode and a second point or said source for maintaining said output electrode more negative than said second point,-a connection between said output electrode and said grid electrode, and a connection including a resistor and a condenser in series between said output electrode and a point or said source more negative than said second point,

the grid voltage of said amplifier.

10. A.- radio signal receiving apparatus which includes a carrier current amplifier having a control electrode and a cathode, a detector tube having a grid, a cathode and an anode, arranged for grid rectification, and connected to the output of said amplifier, a resistor connected in the anode circuit oI-said detector tube, across which is developed a uni-directional rectified voltagewhich causes the voltage at said anode to become less positive upon an increase oi! anode current, a

volume'control tube having a cathode, an input and an output electrode, said input electrode being connected to said anode, whereby variations in the detector anode voltage are impressed on said input electrode, means for causing the cath the eathode 01' said amplifier, a resistor connected between said output electrode and the cathode of said volume control tube, whereby said output electrode becomes more negative when the voltage at said input electrode becomes more positive,

and a connection from said outputelectrode to said control electrode,,whereby an increase of the negative voltage of said output electrode decreases the-amplification of said amplifier.

" '11'. A radio signal receiving apparatus which comprises a carrier current amplifier having a cathode and a control electrode, a detector tube or the grid-detection type having a plate electrode, a volume control tube having a cathode, an input electrode and an output electrode, a resistor connected in the plate circuit of said detector tube, a connection from said input electrode to said plate electrode, means for maintaining the cathode of said volume control tube greatly negative relative to said amplifier cath-' ode, means for maintaining said output electrode slightly negative relative to said amplifier cathode, a resistor connected between said output electrode and the cathode of said volume control tube, and a connection between said output electrode and said control electrode, whereby an increase in-the incoming signal strength creates an increase in the negative 'bias on the control electrode of said amplifier.

12. In a signaling system, a vacuum tube amplifier having a cathode and a control electrode, a second vacuum tube having an anode connected to an intermediate point on a high resistor. means ror'coupling the output of said amplifier to said second tube, a third vacuum tube having a grid, a cathode, an output electrode, a connection from said grid "to' a second intermediate point on said resistor, means for decreasing the anode current in said second tube and thereby positively changin the voltage on said anode in response to an amplified signal, and a direct current connection from the anode of said third tube to said control electrode, whereby the cathode of said detector tube to the junctionot the first and second of said resistors, a connection from the junction oi the second'and third oi. said resistors to said input'electrode, and a direct current connection from said output electrode to said control electrode, whereby the amplification in said amplifier is regulated automatically.

' 14. In a signaling system, a vacuum tube amplifier having a cathode and a control electrode,

a' detector having an anode'connected to an intermediate point on a high resistor, means for coupling, the output of said amplifier to said detector, a vacuum tube having an input electrode connected to a second intermediate point a of said resistor and an output electrode. connected to said control electrode,- means for maintaining said. output electrode normally slightly negative relative to said amplifier cathode, means for changing the anode current in said detector. and thereby changing the voltage on said anode in response to an amplified signal, whereby the amplification in said amplifier is regulated automatically.

15. In a modulated carrier signaling system, a vacuum tube amplifier having a direct current source for supplying the space current thereof and a cathode connected to an intermediate point .of said source, a high resistor connected across said source, a triode detector coupled to the output of said amplifier, said detector/having a cathode connected to said point of said source, and a firstanode connected to an intermediate point on said resistor, a vacuum tulie having/an input electrode connected to a second intermediate point of said resistor which is more negative than said point of said source and an output electrode connected to a control electrode of said amphfier, and means for decreasing the average current of said anode in response increasing signal output of said amplifier, by an amount substantial as compared with the current in said resistor, whereby the amplification in said amplifier is regulated automatically.

16. In a modulated-carrier signaling system, an amplifier tor ampliiyingthe signal, a vacuum tube having a control electrode,.me'ans tor regulating the amplification in said amplifier in proportion to a change of voltage on said control electrode, another vacuum tube coupled ,to the output of said amplifier and having an output electrode, a source of direct voltage for supplying space current to said amplifier, a high resistance path connected between two points 01 substantially difierent voltage on said source, means tor 45 changing the average current of said output electrode in response to increasing signal output of said amplifienby an amount substantial as compared with the current in said path, and two connections from two intermediate points of substantially difierent voltage on said path respectively to said control and output electrodes, whereby the resulting voltage change on said output electrode in response to a signal is partially applied to said control electrode vfor amplifier.

17. In a modulated-carrier signaling system, an amplifier for amplii'ying the signal, a vacuum tube having a control electrode, means for regulating the amplification in said amplifier in proportion to a change or voltage on said control electrode, another vacuum tube coupled to the output oi said amplifier and having an output electrode, a high resistance path having two diiferent intermediate points connected respectively to said control and output electrodes, a common source of direct voltage Ior supplying space current to said amplifier and for maintaining said electrodes at different voltages, and means for causing a change or voltage on said output electrode in response to a signal, by an, amount substantial as compared with the voltage diilerence between said electrodes, whereby a automatically regulating the amplification in said corresponding change of voltage is applied to said control electrode for automatically regulating the amplification in said amplifier.

18. In a modulated-carrier signaling system, an amplifier for amplifying the signal, a vacuum tube having a control electrode. means for regulating the amplification in said amplifier in pro- -portion to a change of voltage on said control electrode, a detector coupled to the output of said amplifier and having an output electrode. a source of direct voltage for supplying space current to said amplifier, a high resistance path connected between two points of substantially difierent voltage on said source, means for changing the average current of said output electrode in response to increasing signal output of said amplifier, by an amount substantial as compared with the current in said path, and two connections from two intermediate points of substantially different voltage on said path respectively to said control and output electrodes, whereby the resulting voltage change on said output electrode in response to a signal is partially applied to said control electrode for automatically regulating the amplification in said amplifier.

19. In a modulated-carrier signaling system, an amplifier for amplifying the signal, a vacuum tube having a control electrode, means for regulating the amplification-in said amplifier in proportion to a change of voltage on. said control electrode, a detector coupled to the output of said amplifier and having an output electrode, a high resistance path having two diiferent intermediate points connected respectively to said control and output electrodes, a common source of direct voltage for supplying space current to response to a signal, by an amount substantial as compared with the voltage difference between said electrodes, whereby a corresponding change of voltage is applied to said control electrode for automatically regulating the amplification in said amplifier.

HAROLD A. WHEELER.

CERTIFICATE OF CORRECTKON.

Patent No. 2,001,950. I May 21, 193s.

HAROLD A. WHEELER.

It is hereby certified thaterror appears in the printed specification of the above numbered patent requiring correction as follows: Page 4, second column, lines 45 and 46, claim 2, strike out the words-"having a cathode, anode and control electrode," and insert the same after "amplifier" in line 43, of said claim; and page 6, second column, line 23, claim 15, for "a first" read an: and in same line and claim for "an" read a first; and that the said Letters Patent should be read with these correctionstherein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 2nd day of July, A. D. 1935.

Leslie Frazer (Seal) 4 I Acting Commissioner of Patents.

DISCLAIMER 2,001,950.Harold A. Wheeler, Great Neck, N. Y. AUTOMATIC VOLUME CoNrRoL. Patent dated May 21, 1935'. Disclaimer filed November 30, 193,5,by the patentee, the assignee Hazeltine Corporation, assenting. Hereby enters this disclaimer to claims 2, 4, 10, and 11 of said patent, which are in the following words:- v

2. A si aling system comprising an amplifier connected to a three electrode detector coup ed to the output of said amplifier having a cathode anode and control electrode, which detector produces a uni-directional change of vo tage dependent on the alternating signal voltage impressed thereon, a volume control tube having a cathode, anode, and control electrode, a connection for coupling the said change of voltage 'to the control electrode of said volume control tube, means for maintaining the cathode of said volume control tube at a potential greatly negative relative to said amplifier cathode, means for maintaining the anode of said volume control tube at a potential normally slightly negative relative to said amplifier cathode, a resistance in series with the anode of said volume control .tube for causing thereon a corresponding change of voltage whereby an increase in the current supplied to said rectifier will produce an increase in the anode-cathode current through said volume control tube, and a connection from the anode of said volume control tube to the control electrode of said amplifier, whereby the amplification of said amplifier is regulated automatically.

4. In a signaling system, a vacuum tube amplifier having a cathode and a control electrode, a vacuum tube detector coupled to the output of saidamplifier, a volume control tube coupled to the output of said detector, said volume control tube having a cathode and an output electrode, means for maintaining the cathode of said volume control tube greatly negative relativeto said amplifier cathode, means for maintaining the out ut electrode of said volume control tube normally slightly negative relative to sai amplifier cathode, means for causing said output electrode to become more negative in the presence of an amplified signal, and a direct current connection between said output electrode and said control electrode, whereby the amplification of said amplifier is regulated automatically.

10. A radio signal receiving apparatus which includes a carrier current amplifier having a control electrode and a cathode, a detector tube having a grid, a cathode and an anode arranged for 'd rectification, and connected to the output of saidamplifier, a resistor connect in the anode circuit of said detector tube, across which is developed a uni-directional rectified voltage which causes the voltage at said anode to become less positive upon an increase of anode current, a volume control tube having a cathode, an input and an output electrode, said input electrode being connected to said anode, whereby variations in the detector anode voltage are impressed on said input electrode, means for causing the cathode of said volume control tubeto be more positive than said input electrode, means for maintaining the cathode of said volume control tube greatly negative relativeto the cathode of said amplifier, means for maintaining said output electrode normally slightly negative relative to the cathode of said amplifier, a resistor connected between said output electrode and the cathode of said volume control tube, whereby 'said output electrode becomes more negative when the voltage at said input electrode becomes more positive, and a connection from said output electrode to said control electrode, whereby an increase of tlfifinegative voltage of said output electrode decreases the amplification of said amp er.

11. A radio signal receiving apparatus which comprises a carrier current amplifier having a cathode and a control electrode, a detector tube of the griddetection type having a plate electrode, a volume control tube having a cathode, an input electrode and an output electrode, a resistor connected in the plate circuit of said detector tube, a connection from said input electrode to said plate electrode, means for maintainin the cathode of said volume control tube greatly negative relative to said amphfier cathode, means for maintaining said output electrode slightly negative relative to said amplifier cathode, a resistor connected between said output electrode and the cathode of said volume control tube, and a connection between said output electrode and said control electrode, whereby an increase in the incoming signal strength creates an increase in the negative bias on the control electrode of said am lifier.

[Oflim'al Gazette ecember s1,-\19s5.1 

